Half Kelly stakes 50% of the amount the full formula recommends. It captures roughly 75% of the growth with about half the volatility, which is why it's the most popular setting.

Kelly Criterion Calculator, Formula & Betting Guide

Q: Is the Kelly Criterion good for betting?

It's mathematically optimal for long-term growth if your probability estimates are accurate. In practice, estimates are imperfect, so most bettors use half or quarter Kelly to reduce volatility and the risk of over-betting.

Q: What is quarter Kelly?

Quarter Kelly stakes 25% of the full recommendation. It's a conservative, beginner-friendly option that further reduces swings at the cost of slower growth.

Q: Can the Kelly Criterion be used for investing?

Yes. In investing and trading it's used for position sizing, deciding how much of a portfolio to allocate to a position based on expected return and probability.

Use the BonusFinder Kelly Criterion calculator to size your bets for maximum long-term growth. Enter your bankroll, the odds, and your estimated win probability, and the tool applies the Kelly formula to recommend how much to stake. Below the calculator you'll find the Kelly formula explained, a worked example, and how to use it for sports betting.

How does this tool work?

The calculator is designed to identify the specific percentage of your total bankroll that you should be staking at a given opportunity.

It is used to prevent players from overbetting on a wager, so you don't risk too much on a single outcome, and to prevent underbetting so you can capitalize on a high value wager.

To get the optimal wager amount you need to factor in three important pieces of information:

Current bankroll: The total amount of money you have to wager
Decimal odds: The odds given to you by a bookmaker, or the ratio of the potential payout
Win probability: Your estimated chance of winning as a percentage

The win probability is the hardest to work out but is also the most crucial.

You will be given the option in the calculator to select your Kelly multiplier. This is done to prevent aggressive strategies for more cautious players that could result in huge swings in your bankroll. You can think of Kelly multipliers like this:

Full Kelly (1.0): This maximizes the growth potential of your bankroll but is highly volatile.
Half Kelly (0.5): What most players choose as it achieves around 75% growth with only 50% volatility.
Quarter Kelly (0.2-0.3): A popular strategy for beginners, dramatically decreasing volatility while providing steady growth.

You can set your Kelly multiplier anywhere between 0.1 and 1.0. What you set it to depends on the amount of risk you're willing to take.

What do my results mean?

A positive result means the calculator is suggesting a percentage of your bankroll to stake. A higher number indicates a more likely winning outcome.

If your results show zero or even negative, this indicates that the odds don't favor any amount based on your estimate and you shouldn't put anything on this.

How to use BonusFinder's Kelly Criterion Calculator

If you would like to view an example of how this tool can be used, please watch our video below:

What Is the Kelly Criterion?

The Kelly Criterion is a formula that tells you how much of your bankroll to stake on a bet or investment to maximize long-term growth.

Developed by John Kelly at Bell Labs in 1956, it sizes each wager according to your edge: the bigger your advantage, the more you stake, and if you have no edge, it tells you to bet nothing.

It's widely used in both sports betting and investing (where it's known as position sizing) because it balances growth against the risk of ruin better than flat-staking.

The Kelly Criterion Formula

The Kelly Criterion formula is:

f* = (bp - q) / b

Where:

f* = the fraction of your bankroll to bet
b = the decimal odds minus 1 (your profit per $1 staked)
p = your estimated probability of winning
q = the probability of losing (1 - p)

In plain terms, the formula weighs your edge against your odds to find the stake that grows your bankroll fastest without over-betting. Our calculator runs this formula for you, so you only need to enter your bankroll, the odds, and your estimated win probability.

Kelly Criterion Example

Say you have a $1,000 bankroll and a bet at decimal odds of 2.00 (+100 in American odds) that you believe has a 55% chance of winning.

b = 2.00 - 1 = 1
p = 0.55, q = 0.45
f* = (1 x 0.55 - 0.45) / 1 = 0.10

The Kelly Criterion recommends staking 10% of your bankroll, or $100. Using half Kelly, you'd bet $50 instead, giving up some growth for far less volatility.

If your estimated win probability were only 50% at these odds, the formula would return zero, meaning you have no edge and shouldn't bet.

Kelly Criterion for Sports Betting

In sports betting, the Kelly Criterion only works if your estimated win probability is more accurate than the sportsbook's odds imply, that gap is your edge.

Because those estimates are rarely precise, most bettors use a fractional Kelly (half or quarter) to protect against overestimating their edge. The biggest risk with full Kelly in betting is that a single overestimated probability can lead to a much larger stake than is safe.

For more ways to plan stakes and bonuses, visit the BonusFinder bonuses tools hub.

Kelly Criterion Calculator

How does this tool work?